As the efforts to recycle post-consumer plastic waste have increased in recent years, so have the demands to make the recycling process as economically feasible as possible. At present, the majority of municipal, mixed post-consumer plastic waste includes polyethylene terephthalate (PET) materials, such as soda bottles, and unpigmented high-density polyethylene (HDPE) materials, such as milk bottles, as well as other materials and types of plastic. Most of the soda and milk bottles are typically removed from the waste stream and reprocessed separately by extrusion to yield separate streams of recycled extruded HDPE and PET.
The remainder of the plastic waste stream includes containers of mixed resin types and pigments, and usually includes a predominance of polyolefins such as polyethylene (PE) and polypropylene (PP), as well as polystyrene (PS), polyvinyl chloride (PVC) and non-soda bottle PET. The remainder of the waste stream may also include other resins, in addition to some PET and HDPE materials which were not selected in the sortation process. The conglomeration of these materials is known as "curbside tailings".
Traditionally, it has been considered economically unfeasible to recycle curbside tailings due to the low-grade nature of the resulting extruded materials. Further, although sorting the curbside tailings plastics might result in a more useful end product, high labor and/or equipment costs make sorting uneconomical. While most efforts in the area of plastics recycling have been focused on the goal of achieving error-free separation of plastics by resin type, a system which efficiently recycles the curbside tailings resulting from an imperfect sortation process into a valuable material is required.
One paper, K. D. Webber, S. A. Swint, T. Conklin and C. I. Chung, Processing of Post-Consumer Commingled Plastics Waste for Consistent and Good Properties, ANTEC '91 at p. 2175-2178 suggests that the addition of certain compatibilizers in a mix which simulates commingled plastics may result in an end product which has a greater impact strength. The paper notes that further research is required to find the "optimum compatibilizer".
The present invention provides methods to meet these needs.